Bound by Two by Kirsten McCurran

A day of painting by a married couple and their longtime friend turns into a night none of them will ever forget! Stacey is just as comfortable with their friend Alex as she is with her husband, Tim. She should be, she's known him just as long, and even dated him first, if only briefly. But that was long in the past, and there has not been anything between Stacey and Alex since, not until too much alcohol and a hot summer day turn their usual flirting into something more. Throw in some teasing about Stacey reading Fifty Shades of Grey, and her husband, Tim, sees an opportunity to make a wild night happen. All he needs is a way to tie Stacey down, and she will be helpless before the two men.